The present invention relates to silicone rubber mixtures, to a process for their preparation and to their use.
It is known to use pyrogenic silica that has been rendered hydrophobic as a filler in silicone rubber mixtures (DE 199 43 666 A1).
U.S. Pat. No. 6,331,588 describes LSR silicone rubber mixtures containing pyrogenic silicas as filler. In order to avoid the undesirable effect of the silanol groups on the mechanical properties of the silicone rubber, it is necessary according to U.S. Pat. No. 6,331,588 to render the surface of the pyrogenic silica hydrophobic.
According to the prior art, in the case of LSR (liquid silicone rubber), either a hydrophilic silica is rendered hydrophobic in situ and at the same time exposed to very high shear forces so that the viscosity and the yield point can be lowered, or a silica that has already been rendered hydrophobic is exposed to high shear forces for the same reason.